GB810535A - Resolution of n-acyl-dl-tryptophans - Google Patents

Abstract

The invention comprises (1) optically active D- and L-lysine salts of D- and L-N-acyl-tryptophans, and (2) the resolution of a mixture of D- and L-N-acyltryptophans by reacting said mixture with D- or L-lysine and fractionally crystallizing the resulting lysine N-acyl-tryptophan salts. The process is preferably applied to the resolution of N-formyl-, N-acetyl- and N-propionyltryptophans, and particularly to racemic forms thereof. The reaction may be conducted in water or an aqueous solvent and the fractional crystallization may be effected in a solvent or solvent mixture in which the lysine N-acyl-tryptophan salts have different solubilities, preferably a mixture of water and a water-miscible organic solvent such as methanol, ethanol or acetone; a mixture of methanol and water in which the proportions of methanol to water is from 3.5-4.5:1 respectively by volume being specified for such purpose. The temperature during fractional crystallization may range from 10 DEG C. to the boiling point of the solvent and is preferably 40 DEG C. or above. The D- or L-lysine and the optically active N-acyl-tryptophans may be recovered from the corresponding lysine N-acyl-tryptophan salts by passing solutions thereof through a cation exchange resin in its H+ or NH4+ form, such resin preferably being a sulphonated copolymer of styrene and divinylbenzene. The recovered lysine may be recycled to the resolution process and the N-acyl-D-tryptophan obtained may be racemized and similarly recycled. The N-acyl-L-tryptophan obtained may be hydrolysed to L-tryptophan by treatment with dilute mineral acid, the resulting hydrolysate being passed through a weakly basic anion exchange resin and the L-tryptophan recovered from the resin effluent. Optically active tryptophan may also be obtained by direct hydrolysis of the optically resolved lysine N-acyl-tryptophan salts with acid or alkali. The examples describe the preparation of L - lysine - N - acetyl - L-tryptophanate and the hemihydrate thereof, N - acetyl - L - tryptophan and L - tryptophan. Reference has been directed by the Comptroller to Specification 745,097.